1. Field of the Invention
The invention relates to a fermentation apparatus.
Although the invention is useful for the fermentation of any vegetable product in the form of a crushed material, the description that follows will refer as an example to winemaking, where the invention has proved particularly effective.
2. Description of Background Art
Winemaking is carried out with the help of special tanks, where the must is introduced to ferment. The fermentation process generates large amounts of gaseous products, especially CO2, participating actively to the success of a good wine. The gases are released from the must and push the marc and every solid part upward where they compact and form a solid layer, called “cap”.
The winemaking methods exploit the fermentation gases, as in WO 98/45403, to mix the cap and prevent solidification thereof. In combination or not, other methods consider to adjust the pressure inside the winemaking tank through safety or degassing valves, both mechanical or membrane valves.
An example of pressure adjustment is described in WO 2006/087601. Here a particular type of degassing valve is used, of the membrane type, in which fluid is pumped to tighten it and lock the vent thereof.
Recently, the applicant has surprisingly discovered how much the pressure inside the winemaking tank is very important, especially during the degassing. Too high a pressure in the tank has immediate repercussions on the quality of wine. The degassing, impulsive or not, induce the must to surface on the cap and the release of gases from within the grape berries. If the pressure is too high, the berries brake and a lot of dregs (mush suspended in the must) is produced. It has been discovered that each grape has its optimum fermentation pressure, which must be regulated with a maximum tolerance of one hundredth of bar (e.g. values as precise as 0.29 bar or 0.31 bar).
The membranes in WO 2006/087601 are made of rubber or similar, and suffer greatly from many factors such as their inertia, whereby they regulate very approximately their venting, or the temperature. A pressure maintained at 0.3 bar during the day can move also to 0.2 bar at night, when the cellar is colder. Moreover, the more the internal pressure of the tank is approaching the threshold pressure, the more sensitivity and precision is lost in the valve, because the membranes are beginning to open. Swinging values with errors of 0.1 bar in WO 2006/087601, which is about 25% of the usual maximum working pressure, are not adequate for a controlled-pressure fermentation. Not only can the must be denatured, but also could the proper fermentation process of grapes be altered through wrong pressures. The same goes for mechanical valves with spring pressure adjustment and calibration.